Disposable devices which are adapted to remove particulates from a fluid flowing through the device have been commercially available for many years. Such devices are commonly referred to as filters. Those of skill in the art have long recognized the fact that filtration devices gradually become loaded or clogged with the particulates that they are designed to entrap. At some point in the life of these filtration devices replacement their filtration efficiency becomes so inefficient as to require replacement. Many of these types of filters are typically retained, out of sight, within a containing chamber. This is easily recognized where, for example, the filter is a furnace filter which is usually retained within the HVAC ducting system. This arrangement makes it inconvenient, if not difficult, for an individual to determine when the filter is in need of replacement. Currently, in many instances, the determination as to whether the filter should be replaced relies upon an "eyeball" inspection to see whether the filtration medium appears to be heavily loaded with particulates. This arrangement can be unsatisfactory for a number of reasons. First, the filter may appear to be heavily loaded but may still have many days or months of effective use left. Removal and replacement of the filter device at this time would not be cost effective in that the filter device would not have been utilized to its fullest extent. On the other hand, the individual performing the visual inspection of the filter may incorrectly determine that the filter has effective life left when such is not the case. A filter device left in, for example, a furnace under such circumstances could well result in damage to the furnace, itself, as a result of the loss of efficiency of the filter and concomitant circulation of particulates through the HVAC system.
Accordingly, a need has existed in the art for a filter device which gives an alert or visual indication that the time for disposal and replacement has come.
Those of skill in the art have previously addressed the situation with, for example, the incorporation of noise makers in the filtration medium. Upon the filtration medium achieving a high particulate load or clogging, the noise maker goes off to give an alert that the filtration device needs replacement. A problem with such a system is that if nobody is currently intent upon filter replacement and no one comes within hearing range of the noise maker, the alert goes unheeded. Because the alert is based upon the filtration device having been generally fully loaded with particulates at the time it went off, problems will occur shortly thereafter. That is, the filter will shortly cease to efficiently function with possible associated damage to any machinery which the filter device was designed to protect by particulate removal.
Another manner in which those of skill in the art have approached the problem is to design filter devices which have extended surface area and thus extended filtration volume. This design is supposed to extend the life of the filtration device to such an extent that maintenance is virtually "guaranteed" prior to exhaustion of the filter's capacity. These designs have, likewise, proven to be less than totally satisfactory.